For operations with the patient in the prone sitting position, an ordinary operating table is fitted with a kneeling attachment such as that illustrated in a brochure entitled "Andrews Spinal Surgery Frame" of Orthopedic Systems, Inc., Hayward, Calif. The Andrews frame, which is currently in widespread use, includes a rigid thigh support having a rail along each side, means pivotably attaching one end of the thigh support to an end of the operating table, a rigid lower-leg-supporting platform including slides riding on said rails, and means for releasably locking the slides to the rails. While a patient is lying on the operating table as shown in FIG. 9 of the brochure, the attachment is pivoted downwardly as shown in FIG. 12 to place the patient in the prone sitting position. Usually the patient's backbone should be horizontal, and to adjust the attachment to do so, the Andrews frame includes a rack-and-pinion drive for sliding the lower-leg platform up and down along the rails of the thigh support. Partly because of the rack-and-pinion drive, the Andrews frame is exceedingly heavy and hence is wheeled about on a cart as shown in FIG. 2 of the brochure.
Kneeling attachments which are more or less similar to that of the Andrews brochure are shown in U.S. Pat. Nos. 2,577,177 (Anderson); 3,372,921 (Anderson); 2,895,775 (McDonald et al.); 3,289,674 (Platt); 4,391,438 (Heffington); and 4,398,707 (Cloward). Some of these incorporate mechanisms which like that of Andrews mechanically raise the lower-leg platform. For example, McDonald's includes a screw along each side of the thigh support. In others such as Cloward's which have no such mechanism, it would be unreasonable to attempt to raise or lower the lower-leg platform without first freeing it from the patient's weight.
When in the prone sitting position, the patient's lower legs usually rest on a flat cushion on a flat platform. For example, see the cushion 71 in FIG. 1 of U.S. Pat. No. 2,577,177 (Anderson); the cushion 22 in FIG. 1 of U.S. Pat. No. 3,643,938 (Levasseur); and the cushion 42 in FIG. 1 of U.S. Pat. No. 4,398,707 (Cloward). The same arrangement is illustrated in the aforementioned "Andrews Spinal Surgery Frame" brochure. During an operation using the Andrews frame, the patient's lower legs are necessarily securely strapped to the lower-leg platform, usually together, making it awkward to release either leg should it be desired to move that leg. The weight of the patient's hip area largely bears on the kneecaps which can become inordinately uncomfortable in a long operation.
Instead of being flat, the lower-leg platform of U S. Pat. No. 3,289,674 (Platt) comprises "L-shaped supporting frames 70 and 71, respectively, which are each provided with suitable padding 72 for the comfort of the patient" (col. 4, lines 32-36). Somewhat similar to the padded L-shaped supporting frames of the Platt patent are the kneeling frames pictured at page 13 of a brochure entitled "The Maquet Operating Table System", Catalogue No. 1120 of Stierlen-Maquet AG, Rastatt, Federal Republic of Germany. While that picture lacks details, Maquet's kneeling frames (as compared to those of the Platt patent) have deeper depressions which appear to be contoured to provide lateral support for much of the lower leg. Like the flat cushions cited above, both Maquet's and Platt's kneeling frames appear to entail considerable weight on the kneecaps.
When a patient is in the prone sitting position, the buttocks usually rest against a seat pad as shown in the aforementioned "Andrews Spinal Surgery Frame" brochure. As also illustrated there, the buttocks may be laterally supported by two cylindrical cushions, but often have no lateral support, as in U.S. Pat. No. 4,391,438 (Heffington). Instead of using cushions, straps may be wrapped around the thighs, either in combination with a seat pad or without as in U.S. Pat. Nos. 3,643,938 (Levasseur) or No. 2,577,177 (Anderson).